Exhaust treatment systems may be used to reduce or remove components of the exhaust of internal combustion engines. Exhaust emission standards for internal combustion engines have become increasingly rigorous, and manufacturers have developed exhaust treatment systems to reduce the amount of certain components in the exhaust. For example, the amount of nitrogen oxides (NOx) emitted from an engine may be limited by environmental regulations. For example, some exhaust treatment systems for diesel engines may discharge diesel exhaust fluid (DEF) into the exhaust stream to reduce the amount of NOx in the exhaust. DEF is a solution of urea and water (generally 32.5% chemical-grade urea and 67.5% de-ionized water) that is discharged into a mixing zone of an engine exhaust pipe upstream of a catalyst of a selective catalytic reduction (SCR) system. The exhaust with the NOx heats the DEF and causes the DEF to break down into ammonia (NH3) and carbon dioxide (CO2). As the NOx and ammonia pass over the catalyst, the NOx and ammonia react to produce nitrogen (N2) and water.
Diesel engine exhaust treatment systems often include a large reservoir for storing the diesel exhaust fluid and a pump for withdrawing the diesel exhaust fluid from the reservoir. The pump advances the diesel exhaust fluid to a nozzle, which discharges the diesel exhaust fluid into the mixing zone of the exhaust pipe. For example, U.S. Pat. No. 8,967,181 discloses a diesel engine exhaust fluid system pumps fluid from a diesel exhaust fluid tank to a fluid-discharge nozzle coupled to a mixing zone of an exhaust pipe.
In some applications, the mixing zone of the exhaust pipe is located relatively far away from the reservoir of the system. The pump of the system therefore needs to be sufficiently powerful to pump the diesel exhaust fluid from the reservoir to the mixing zone. However, larger pumps capable of pumping the diesel exhaust fluid to the mixing zone may not provide high accuracy and fine adjustment of the volume of diesel exhaust fluid discharged into the mixing zone.